Automatic reclosing circuit breaker



Sept. 18, 1956 J. M. WALLACE ET AL 2,

AUTOMATIC RECLOSING CIRCUIT BREAKER 2 Sheets-Sheet 1 Filed Feb. 10, i951QEEQ ii Fig.3.

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Insulation Insulation INVENTORS WITNESSES: zayj JomesMWolloce andHerbert L.Rowlins,deceosed ministroirix.

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ATTOR EY by Charlotte M.Rcwlins,Ad

Sept. 18, 1956 J. M. WALLACE ETAL AUTOMATIC RECLOSING CIRCUIT BREAKER 2Sheets-Sheet 2 Filed Feb. 10, 1951 W W d'w mm B r m n M Wd M 3m madWITNESSES: {4 2 United States Patent AUTOMATIC RECLOSIN G CIRCUITBREAKER James M. Wallace, Pittsburgh, Pa., and Herbert L. Rawlins,deceased, late of Pittsburgh, Pa., by Charlotte M. Rawlins,admiuistratrix, Pittsburgh, Pa., assignors to Westinghouse ElectricCorporation, East Pittsburgh, Pa., a corporation of PennsylvaniaApplication February 10, 1951, Serial No. 210,387 14 Claims. (Cl.200-89) Our invention relates generally to automatic reclosing circuitbreakers, and it has reference in particular to automatic reclosingcircuit breakers of the air break type.

One object of our invention is to provide a compact and inexpensivereclosing circuit breaker.

Another object of our invention is to provide in a reclosing circuitbreaker for utilizing energy from an overload condition to introduce anormal gap in the circuit for a predetermined number of operations, andthen efiect lockout with a greater than normal gap in the circuit.

Yet another object of our invention is to provide an automatic reclosingair circuit breaker construction in which a movable contact is actuatedin a predetermined path for a predetermined number of times to open thecircuit in response to an overload, whereupon releasable means isoperated to introduce a greater than normal gap in the circuit.

It is also an object of our invention to provide a large clearanceacross the open gap of a reclosing circuit breaker in the lockoutposition by means of releasable lockout means.

We also provide as one aspect of our invention, for utilizing abimetallic latch element as part of a latch mechanism for releasing theoperating mechanism of a reclosing circuit breaker from a normalposition so as to provide an increased air gap in the circuit.

It is also an important object of our invention to provide a reclosingcircuit breaker construction wherein a movable contact element operatesto release the operating .mechanism from a normal position to a lockoutposition.

Another important object of our invention is to provide in an automaticreclosing air circuit breaker, for utilizing thermally responsive meansfor releasing the operating mechanism to a lockout position after apredetermined number of circuit interrupting operations.

A further object of our invention is to provide in a reclosing circuitbreaker of the air break type, for utilizing a solenoid to operate amovable contact member for interrupting the circuit a predeterminednumber of times and then utilizing the movable contact member forreleasing the reclosing mechanism to a lockout position.

Another object of our invention is to provide in a circuit breaker ofthe air-break type, for utilizing a movable contact member with ansingularly-shaped section which moves in an angularly-shaped slot in agas generating arc interrupter, so as to provide as narrow an arcextinguishing slot as possible While providing sutficient rigidity forthe contact member.

It is also an object of our invention to provide for pivotallysupporting the operating mechanism of a reclosing circuit breaker sothat it may be released to a non-circuit completing position.

Other objects will, in part, be obvious and will, in part, be explainedhereinafter.

For a more complete understanding of the nature and the scope of ourinvention, reference may be made to the following detailed description,which may be read in connection with the accompanying drawings, inwhich:'

Figure 1 is a side elevational view partly in section, of a reclosingcircuit breaker embodying the invention in one of its forms;

Fig. 2 is a bottom plan view of the circuit breaker shown in Fig. 1;

Fig. 3 is aside elevational view in section of a reclosing unit for areclosing circuit breaker embodying the invention in a different form;

Fig. 4 is a partial side elevational view of a circuit breaker showingone method of mounting for the upper end of the circuit breakerreclosing unit shown in Fig. 3; and

Fig. 5 is a sectional view taken along the line VV of Fig. 3.

Referring to Fig. 1, the reference numeral 10 may designate generally anautomatic reclosing air circuit breaker comprising a movable contactmember or rod 12 and an operating mechanism 14 disposed to be mounted onan insulating support 16 for engaging a stationary contact jaw 18mounted in an arc interrupter 20 supported by an insulating support 22.The insulating supports 16 and 22 are insulators, preferably ofporcelain or the like, and may be mounted on a suitable base (not shown)such as a channel base commonly used for disconnecting switches.

The interrupter 20 may comprise a metal cap 24 which may be fixedlymounted on the insulating support 22 by means of a suitable bracket 26.A terminal 27 may be secured to the bracket 26 for making electricalconnection with the stationary contact member 18, which may be :mountedinside the cap 24. In order to provide for extinguishing an are whichmay be drawn between the movable contact member 12 and the stationarycontact member 18, the interrupter 20 may comprise a body of fiber orsimilar gas generating material 28 having a central passage 29 thereinfor receiving the moving contact rod member 12. The body member 28 maybe mounted in the cap 24 in any suitable manner being, for example,threaded thereinto.

The operating mechanism 14 may comprise a cylindrical case 30 of amagnetic material such as iron or steel, within which may be disposed anoperating coil 32 for actuating the movable contact member 12 to efiecta circuit interrupting operation. The contact rod member 12 may,

for example, comprise a cylindrical rod at least the lower portion ofwhich may be of a magnetic material and which may be slidably disposedin an insulating tube 34 positioned within the operating coil 32. Anextension 35 may be provided on the lower end of the rod 12, and an;opening 33 may be provided adjacent the upper end, for

purposes to be explained hereinafter. A spring 36 may be disposed withinthe tube 34 for normally biasing the contact member 12 into engagementwith the stationary contact jaws 18. Spring contact fingers 37 may beprovided for effecting an electrical connection between the coil 32 andthe contact member 12 being, for example, mounted on the upper end ofthe coil 32 and connected thereto by means of a conductor 38. The tube34 may be partially closed at its lower end, being, for example,provided with an orifice 39, which may be normally closed by means of avalve member 40 biased by means of a spring 42 so as to close theorifice 39 against the movement of air therethrough into the tube 34. Aplurality of metered orifices 43 may be provided in a plate 45,otherwise closing the lower end of the case 30 and the tube 34 forcontrolling the rate of escape of air from within the tube 34, and hencethe rate of downward movement of the contact rod member 12, which may bedisposed to provide a relatively snug fit within the tube. An annularshoulder 46 may be provided around the contact member 12 for engagementwith the contact fingers 37 so as to limit upward movement of thecontact member 12.

The case 30 may be pivotally supported on the insulating support 16 bymeans of a trunnion mounting 48 which may be supported on the insulatorsupport 16 in insulated relation to a terminal 53, being separatedtherefrom by sulating support 16 and insulated from the trunnionmounting 48 by insulation 54. A spring 55 may be utilized to normallybias the latch member 52 to the position shown in which it engages theadjacent edge of the case 38. A bimetallic operating member 57comprising laminations ofmetals having different coeflicients ofexpansion may be secured to the latch member 52 and connected in circuitrelation with the case 30 by means of a metallic contact member 58mounted on the latch member 52. A shunt 59 may be provided forconnecting the end of the operating member 57 which is remote from thelatch member to the connector 53.

The operating member 57, as shown intFig. 2, may be normally disposed toone side of an extension 60 on the valve member 40. After a plurality ofcircuit interrupting operations, the operating member 57 will besurficiently deflected by the heat generated by the flow of faultcurrent therethrough, so as to deflect away from the material having thegreater coefficient of expansion, and thus engage a stop 62, whereuponit will be positioned in the line of movement of the extension 60, so asto be engaged thereby when the contact member 12 is pulled downwardlyduring a circuit interrupting operation, and the extension 35 engagesthe valve member 40 for rotating the latch member 52 in a clockwisedirection. A' spring '64 will thereupon be rendered effective to rotatethe operating mechanism in a clockwise direction about the pivots 49, sothat the contact member 12 will no longer be eifective to complete acircuit making operation' when it is biased upwardly by the spring 36.

With the reclosing circuit breaker in the normal opcrating position, asshown, an electric circuit may be traced therethrough, extending fromterminal 27 through bracket26, cap 24, stationary contact jaws18,movable contact rod member 12, spring contactl fingers 37,

conductor '38, operating coil 32, conductor 66, case 30, latch contactmember 58, bimetallic operating member 57, and shunt 59 to terminal 53.

While the circuit breaker conducts current below the normal rating, theoperating coil 32'has no appreciable effect on the movable contact rod12. Should the cur-' rent carried by the circuit breaker exceed thenormal rating, the operating coil 32 will be effective to draw thecontact rod' 12 downwardly against the force of the biasing spring 36sufliciently to clear the lower end of interrupter body 28, thusinterrupting the circuit to the contact member 18. Any are drawn betweenthe moving contact member 12 and the stationary contact member 18 willbe drawn into the relatively narrow passage 29 in the interrupter 20.Gases generated from the surface walls of the opening 29 of theinterrupter as a result of heat from the are, blast through the opening29 and assist in rapidly extinguishing the are, thus effectivelyinterrupting the circuit. During the flow of current in excess of thenormal rating, the bimetallic operating element 57 will be affected bythe heat therefrom and warped in the direction of the path of movementof the extension 60. Downward movement of the contact member 12 will belimited only by the rate of flow of air through theorifice 43, since thevalve member 40 operates to release air from the tube 34. Upwardmovement or the contact member 12 will, however, be delayed, since thevalve member'40 seals off the lower end of the tube 34 and upwardmovement of the contact rod member 12 will be determined by the rate ofleakage of air between the contact member and the walls of the tube.

Should the fault continue, greater than normal current will again flowupon engagement of the contact rod member 12 with the stationary contactmember 18, and the operating coil 32 will again be rendered effective todraw the contact rod member 12 downwardly to interrupt the circuit. Thebimetallic operating member 57 will again be heated by the fault currentand will be warped further into the path of movement of the extensionas. After a predetermined number of operations of the circuit breaker ininterrupting the circuit, for example, upon the fourth circuitinterrupting operation, the bimetallic operating member 57 may engagethe stop 62. Just before the contact member 12 reaches its furtherestdownward posi tion, in which it clears thelower end of fiber block 2%,the valve member 40 will be actuated by the extension 35 thereof, andthe extension as will strike the deflected operating member 57, so as torotate the latch member 52 in a clockwise direction. The operatingmechanism 14 will thereupon be free to rotate in a clockwise directionunder the influence of the spring 64, so as to move the contact rodmember 12 out of alignment with the stationary contact jaws into thelockout position. This renders the movable contact member ineffective tocomplete the circuit when it is returned to its uppermost position bythe spring 36, and places a relatively large air gap between the contactmembers 12 and 18 when the operating mechanism is in the lockoutposition.

, The recloser may be reset by inserting a hook stick in the opening 33,and pulling the contact rod 12 downwardly, while urging it pivotally ina counter-clockwise direction. When the upper end of the rod 12 isaligned with the opening 29, the hook stick may be withdrawn, and thespring 36 will urge the rod into engagement with stationary jaws 18, toreclose the breaker.

Referring to Fig. 3, it will be seen that the operating mechanism 14'and the interrupter 2%, instead of comprising separate structures, maycomprise a single recloser unit 6?, being mounted in a common case "iii,comprising for example, a cylindrical case of insulating material whichmay be threaded adjacent opposite ends to receive metallic terminal caps72 and 74. The cap 72 may be provided with stationary contact jaw member73 disposed to engage the lower end of a movable contact member 75disposed to be actuated by an armature 12. The movable contact membermay be normally biased into engagement with the stationary contactmember by means of a spring 36 and may be withdrawn from engagementtherewith by means of an operating coil 32 which actuates the armature12.

In order to provide the maximum arc interrupting effect, the contactmember 75 may, as shown in Figs. 3 and 5, have an angularly-shapedcross-section, and the body 76 of fiber or other gas-generating materialsurrounding the contact member may be provided with a relatively snuglyfitting angularly-shaped slot 77 therein for receiving the contactmember so as to provide as narrow a slot as possible and yet maintain asufficiently rigid contact member.

The operating coil may be connected in series circuit relation with thecontact member 75 by means of a sliding spring contact finger 78 mountedon the lower end of the operating coil 32 and a conductor 79. The lowercap 72 may be provided with pivot lugs 49 on the opposite sides thereoffor mounting in a trunnion bracket similar to the bracket 48 of Fig. 1,except for the insulation 47 and 54 which may be omitted, so as topivotally mount the reclosing circuitbreaker unit. The upper cap 74 may,as shown in Figs. 3 and 4, be provided with a projection 80 disposed tobe engaged in locking relation with a releasable latch member 32, whichmay be tube.

pivotally mounted in a sleet hood 84 on the upper insulatingsupport 22by means of a bracket 85. The latch member 82 may be normally biasedinto engagement with the projection 80 by means of a spring 86 and mayhave a bimetallic operating member 88 comprising laminations of metalshaving difierent coefiicients of expansion disposed side'by side,mounted thereon. The latch member 82 may, for example, comprise a blockof insulating material having the operating member 88 secured thereto ona contact member 94 which is disposed to engage the projection St Asuitable shunt 92 may be provided for connecting the free end of theoperating member to the connector 27. A spring 94 may be provided forbiasing the cap 74 in a clockwise direction when it is released by thelatch member 82.

Referring to Figs. 3 and 4, a circuit may be traced through thereclosing circuit breaker extending from the terminal 27 through shunt92, bimetallic operating member 88, contact member 90, projection 80,cap 74, spring contact member 93, operating coil 32, conductor 79,contact spring member 78, armature 12', contact member 75, stationarycontact member 73 and the cap 72 to the pivots 49 by means of whichconnection may be made to trunnion bracket 48 and the lower connector53.

So long as normal current flows through the circuit breaker, the movablecontact member 75 remains in contact with the stationary contact member73. Should the current exceed the normal value, the operating coil 32will effective to retract the armature 12' and movable contact member75, thus interrupting the circuit at the stationary contact member 73.The are will be drawn into the relatively narrow angular slot in thebody member 76 and the gases generated from the walls of the slot 77' bythe heat of the arc will be effective in rapidly extinguishing the arc.

Upward movement of the contact member will be limited only by the rateof passage of air through the metering orifices 43 in the upper cap,since the valve member 4t) readily permits escape of air from within thetube 34. Downward movement of the contact member 75 to reclose thecircuit will be limited by the dashpot action of the armature 12 in thetube 34, since the valve member 4t closes to prevent the admission ofair to the The rate of movement of the contact member 75 in reclosingthe circuit will thus be determined by the rate of leakage of airbetween the armature and the tube.

Upon the flow of fault current, the bimetallic operating member 855,which is normally positioned to one side of the extension 6%) or" thevalve member 42, will be deflected towards the path of the extension.After a predetermined number of reclosures, for example, threereclosures, the bimetallic operating member will be deflected into thepath or the projection 60. Thus,when the contact member "75 interruptsthe circuit for the fourth time, the valve member 40 will be actuatedthere by the extension 35 thereof to engage the operating member 88. Thelatch member 82 will thereby be actuated in a. counterbalance directionso as to release the projection. 80. The reclosing circuit breaker unitin the casing 70, including the interrupter and operating mechanism,will therebetween be actuated by the spring 94 in a clockwise directionso as to introduce a relatively large air gap between the end cap 74 andthe connector 27, so that upon the return of the contact member 75 intoengagement with the stationary contact member 73 the circuit breaker isno longer effective to complete the circuit, and is disposed in itslockout position. The breaker may be reclosed by inserting a hook stickin an eye 96 and urging the unit 69 in a counterclockwise direction toreengage latch member 82 and projection 80.

From the above description and the accompanying drawings, it will beapparent that we have provided in a simple and effective manner forinterrupting an electric circuit by means of a reclosing air circuitbreaker. We have provided for normally introducing a predetermined 6 gapin the circuit when it is interrupted, and for increasing the amount ofthe gap When the circuit breaker has operated a predetermined number oftimes and operates to its lockout position. By releasably supporting theoperating mechanism of the reclosing circuit breaker on a lower supportin a circuit completing position, and releasing it from this position toa position in which it is no longer effective to complete the circuit, asimple and inexpensive reclosing circuit breaker construction isprovided. By utilizing the moving contact member to eitect release ofthe operating mechanism from its normal operating position to thelockout position, positive protection is provided against operation ofthe mechanism to the lockout position, except when the circuit breakeris in the open position.

Since certain changes may be made in the above-described constructionand difierent embodiments of the invention may be made without departingfrom the spirit and scope thereof, it is intended that all the mattercontained in the above description and shown in the accompanyingdrawings, shall be considered as illustrative and not in a limitingsense.

' We claim as our invention:

1. An automatic reclosing circuit breaker comprising, spaced terminals,means separably connecting said terminals including an operatingmechanism having an elongated longitudinally movable contact membernormally biased to a circuit making position between said terminals andelectroresponsive means energizable to actuate the movable contactmember longitudinally to a circuit opening position, support means forsupporting said operating mechanism for movement relative to one of saidterminals, a latch releasably securing said operating mechanism inpredetermined relation to said one terminal, and operation countingmeans operable to cause release of said latch in response to apredetermined operation of the electroresponsive means, said countingmeans being mounted on one of the terminals independently of theoperating mechanism.

2. In an automatic reclosing circuit breaker, a pair of terminals, meansconnecting said terminals including a longitudinally movable contactrod, electromagnetic means operable to move said rod to effectinterruption of the connection between the terminals in response to anoverload condition, support means for supporting said electromagneticmeans and rod for pivotal movement relative to one of the terminals,releasable means disposed to secure the electromagnetic means and rod inpredetermined aligned relation to said one terminal, and electrothermalmeans movable in response to an overload condition to provide anoperative connection between the electroresponsive means and thereleasable means in response to a predetermined number of operations ofthe electroresponsive means and cause operation of the releasable meansto release said electroresponsive means for movement relative to saidone terminal.

3. An automatic reclosing circuit breaker comprising, spaced terminalmembers, means separably connecting the terminal members includingrelatively movable contact means normally biased into contact makingposition to complete a circuit between the terminal members,electroresponsive means including a solenoid operable to effectseparation of said contact means to interrupt the circuit between theterminals in response to predetermined circuit conditions, a housing forthe electroresponsive means, support means pivotally supporting saidhousing and electroresponsive means including the solenoid on one of theterminal members for movement relative thereto, releasable meansnormally operable to maintain said housing and electroresponsive meansin predetermined positional relation with said one terminal membermeans, and operating means for said releasable means disposed to beactuated only after a predetermined number of separations of saidcontact means to release said electroresponsive means from saidpredetermined positional relation.

.4, A circuit interrupter comprising, spaced apart terminals, meansseparably connecting said terminal members including movable contactmeans, are extinguishing means including a gas evolving material havinga passage through which the movable contact mean moves, electromagneticmeans operable to actuate the movable contact means to withdraw it fromsaid passage and interrupt the circuit between the terminals in responseto an overload in said circuit, means for effecting return of saidcontact means following an interruption, support means disposed to mountsaid electromagnetic means and said contact means on oneof saidterminals for predetermined movement relative thereto, releasable meansnormally securing said electromagnetic means is predetermined positionalrelation with said one terminal, and means pro viding an operativeconnection between the electroresponsive means and the releasable meansfor at times causing the electromagnetic means to actuate saidreleasable means 'to release saideiectromagnetic means.

5. A circuit interrupter comprising, a stationary contact, alongitudinally movable contact, support means pivotally supporting themovable contact for pivotal movement, electroresponsive means operableto move the movable contact longitudinally away from the stationarycontact to effect a circuit interrupting operation, means normallybiasing the movable contact into engagement with the stationary contactto efiect engagement of the contacts following a separation, releasablemeans normally operable to maintain the movable contact in predeterminedalignment with said stationary contact, and counting means actuatingsaid releasable means to release said movable contact from alignmentwith said stationary contact only in response to a predetermined numberof circuit interrupting operations of said electroresponsive means.

6. In an automatic reclosing circuit breaker, a pair of terminals, alongitudinally movable contact, means biasing said contactlongitudinally in one direction into circuit making relation with one ofsaid terminals, electroresponsive means operable to move the movablecontact longitudinally in the opposite direction out of circuit makingrelation with said terminal in response to an overload condition,support means pivotally supporting said movable contact, a latchnormally operable to maintain the movable contact in predeterminedlongitudinal alignment with said terminal, and operating means disposedto release said latch in response to operation of said movable contactafter it has operated a predetermined number of times.

7. A circuit interrupter comprising, a movable contact rod normallybiased to a circuit completing position, electromagnetic means operableto move said contact rod longitudinally to a circuit interruptingposition, said contact normally returning to the circuit completingposition following a circuit interrupting operation, releasable meansnormally operable to maintain the movable contact in an aligned positionin which it can effectively complete a circuit following aninterruption, said releasable means having a part movable in response toa predetermined number of such circuit interrupting operations of themovable contact member to provide an operative connection between theelectroresponsive means and the releasable means for permitting saidelectroresponsive mean to actuate said releasable means to release themoving contact member fromsaid circuit completing aligned positionwhereby it is prevented from completing said circuit.

'8. An automatic reclosing circuit breaker comprising, a housing,pivotal support for said housing, contact means disposed in said housingincluding a movable contact member operablein one position of thehousing to complete an electric circuit with'a fixed con'tact,electroresponsive means operable in response to an overload in saidcircuit to actuate the movable contact memberto inter- 8 i rupt saidcircuit, biasing means opposing said electroresponsive means, releasablemeans normally operable to retain. said housing and contact memberaligned for completing the circuit, and means operable in response to apredetermined number of such circuit interrupting operations to permitthe electroresponsive means to actuate said releasable means to releasethe housing and movable contact member from circuit completing alignmentwhereby the biasing means is ineifective to efiect completion of thecircuit.

9. An interrupter comprising, a stationary contact, an elongated contactmember movable longitudinally to engage the stationary contact member,electroresponsive means operable to actuate the movable contact memberlongitudinally away from the stationary contact member and interrupt acircuit in response to an overloaded condition, support means pivotallysupporting the movable contact member for movement away from saidstationary contact about a transverse axis, latch means normallyoperable to retain the movable contact in alignment with the stationarycontact during a circuit interrupting operation, and electroresponsiveoperating means operable to eifect release of the latch means after apredetermined number of circuit interrupting operations.

10. A circuit interrupter comprising, a pair of contacts, one of saidcontacts being movable relative to the other, a gas evolving materialhaving an opening to receive a portion of the movable contact member,electroresponsive means operable to actuate said member and withdraw itfrom said opening in a circuit interrupting operation, means actuatingsaid movable contact member in one positional relation to engage theother contact following a circuit interrupting operation, releasablemeans normally operable to maintain the movable contact member inalignment with said opening for said one positional relation, and meansoperable in response to a predetermined number of circuit interruptingoperations to operate said releasable means whereby the movable contactmember is released from said aligned positional relation.

11. A circuit interrupter comprising, a first support, stationarycontact means mounted on said support, a body of gas evolving materialmounted on said support and having a passage therethrough aligned withsaid contact, a second support in spaced relation with said firstsupport, elongated contact means, guide means slidably supporting theelongated contact means for longitudinal movement, latch means operableto maintain the guide means with the elongated contact means alignedwith the stationary contact means, means pivotally supporting the guidemeans for pivotal movement about an axis transverse of the elongatedcontact means, electroresponsive means operable to efiect longitudinalmovement of said elongated contact means away from the stationarycontact means in response to predetermined circuit conditions, andoperating means operable to release said latch means after a number ofcircuit opening operations.

12. In an automatic reclosing breaker, separable contact means, a casinghaving guide means supporting one of said contact means for movementalong a predetermined path, means biasing said contact means together,electromagnetic means operable to separate said contactmeans to effect acircuit interruption, latch means normally operable to retain the casingin a predetermined position in which the movable contact is effective toperform a circuit closing operation, means biasing the casing away fromsaid position,. and operating means for the. latch means including anoverload responsive member movable to a position such that theelectromagnetic means engages and operates the latch means through theoverload responsive member to release the casing from said positionafter a predetermined number of circuit interrupting operations.

13. A circuit interrupter comprising, an insulating container havingconducting cap means adjacent each end, a movable contact, guide meanslocating the movable contact within the container for circuit makingconnection with one of said cap means at the end of the container, meansbiasing the movable contact into contact with said one cap means, asolenoid disposed in the container to actuate the movable contact out ofcircuit making connection with said cap means, support means pivotallysupporting the container at one of said cap means, a connector,releasable means disposed to secure the other cap means in circuitmaking relation with said connector, and operating means having abimetallic element actuated by an over-current to effect release of thereleasable means by movement of the movable contact to release said capmeans from circuit making connection with said connector.

14. In a circuit interrupter, an operating mechanism including a movablecontact member and electro-responsive means energizable to actuate themovable contact member to a circuit opening position, a casing for saidoperating mechanism, support means for said operating mechanism,releasable means disposed to secure said casing in predeterminedoperating relation to said support means, and operation counting meanshaving a part movable to a position where it is actuated by theelectroresponsive means for causing release of said releasable meansdisposed on said support means externally of said casing.

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